I thought tend (used to imply “regularly or frequently behaving in a particular way or having a certain characteristic – Oxford’s def; 1.1) always has to be used with the to-infinitive form of verbs.
Today, however, I encountered this example:
Most meta-analyses show that, with some exceptions, well-established psychotherapies tend be approximately equivalent in efﬁcacy (Wampold, Mondin, Moody, Stich, Benson, & Ahn, 1997).
And while I couldn’t find anything regarding tend in regards to these two forms (with or without “be”), searching .edu domains precisely for "tend be" returns some 12,000 results. E.g.:
Fungal-like protists and the Chytridiomycota tend be aseptate, except to delimit reproductive or specialized cells (such as sporangia and gametangia).
The disadvantages of physical sunscreens is that they tend be thicker and look a little white on the skin.
[The book] reveals that readers [...] tend be more open to diversity; politically tolerant; less authoritarian; less likely to support the use of deadly force or torture; more politically active; and are more likely to have a negative view of the Bush administration.
It has long been appreciated that genes that perform core functions tend be more conserved in amino acid sequence over long evolutionary time periods.
So, is it ok to write “tends be” instead of “tends to be”?